The invention relates to a circuit breaker applied to a circuit breaker or an earth-leakage breaker for a low-voltage circuit. More specifically, the invention relates to a switching device equipped with an isolation function for preventing an operation handle from moving to an OFF position in a state that main-circuit contact points are stuck due to an abnormal current.
FIG. 5 shows a configuration of a circuit breaker as an example. In the figure, reference numeral 1 denotes a case (mold case) of the circuit breaker, reference numeral 2 denotes a main-circuit terminal at a power-source side, reference numeral 3 denotes a main-circuit terminal at a load side, reference numeral 4 denotes a fixed contact, reference numeral 5 denotes a movable contact, reference numeral 6 denotes an earth-leakage breaker, reference numeral 7 denotes a contact holder for the movable contact 5, reference numeral 8 denotes a switching device, reference numeral 9 denotes a switching operation handle, and reference numeral 10 denotes a bimetal-type over-current tripping device.
The switching device 8 has a configuration wherein the following constituent members are assembled to an assembly frame (side plate) 18 of the switching device: a swing-type switching lever 11 connected to the handle 9; a toggle linkage 15 having a link shaft 14 for connecting an upper link 12 and a lower link 13, and bridging between the movable contact 5 and a latch (trip lever); a tripping device 16 formed of a lever-shaped latch 16a and a latch receipt 16b for releasing the latch 16a in response to a movement of the over-current tripping device 10; and an operation spring (tension coil spring) 17 tightly stretched between the switching lever 11 and the link shaft 14 of the toggle linkage.
An operation of switching the circuit breaker is well known. When the handle 9 is operated to move from the ON position to the OFF position shown in the figure, the upper link 12 and the lower link 13 of the toggle linkage 15 are folded or bent by a spring force of the operation spring 17, and the movable contact 5 is opened in conjunction with the folding.
When an over-current flows in an electrified state to activate the over-current tripping device 10, an output of the over-current tripping device 10 activates the tripping mechanism 16 to release the latch 16a latched by the latch receiver 16b. As a result, the latch 16a rotates counterclockwise, and the switching device 8 performs tripping, so that the movable contact 5 is opened to cut off the current. In addition, as a result of the tripping, the handle 9 moves together with the switching lever 11 to an intermediate position between the ON position and the OFF position, thereby indicating the occurrence of the tripping. In order to turn on the circuit breaker again after the tripping, it is necessary only to move the handle 9 to the OFF position temporarily to reset the tripping mechanism 16, and then move the handle 9 back to the ON position to close the movable contact 5.
In the circuit breaker, the fixed contact point and the movable contact point may be stuck when an abnormal current flows through the main circuit in the electrified state and the main-circuit contact points are closed. In this case, even though the over-current tripping device 10 operates normally, the movable contact 5 is not opened, and the main-circuit contact points remain in contact. Incidentally, the handle 9 stops at the ON position in this state.
Further, in the structure of the switching device described above, when the main-circuit contact points are stuck, it is still possible to move the handle 9 from the ON position to the OFF position by applying a force greater than usual to stretch the operation spring 17. Therefore, an operator may move the handle to the OFF position without knowing the abnormal state in which the contact points are stuck. In this case, if the operator mistakenly acknowledges that the breaker is disconnected, and performs maintenance and repair on the load side, there is a risk that the operator may touch a hot line and receive an electric shock.
In order to prevent such an electric-shock accident, a circuit breaker may be provided with a function (called “isolation function”) for making it impossible to move the handle to the OFF position when the contact points are stuck during the electrified state. As an example of a mechanism having the function, Japanese Patent Publication (Kokai) No. 01-36652 has disclosed a configuration in which a blocking member is provided between a switching lever of a switching device and a link node (link shaft) of a toggle linkage for engaging or abutting against the components.
However, the configuration disclosed in Japanese Patent Publication (Kokai) No. 01-36652 has the following problems in terms of design and manufacture. That is, in the disclosed configuration for preventing the handle from moving to the OFF position when the contact points are stuck, a blocking mechanism is formed of the link shaft of the toggle linkage and the notch formed in the switching lever at a side opposite to the link shaft or a folded engagement part formed at a side edge of the switching lever. When the contact points are stuck, the notch formed in the switching lever or the folded engagement part engages or abuts against the link shaft of the toggle linkage, so that the handle is not moved to the OFF position.
In the configuration described above, the link shaft of the toggle linkage needs to directly engage or abut against the notch or folded engagement part formed in the switching lever. Thus, it is necessary to carefully consider a shape of the notch or folded engagement part and a position of the link shaft, thereby creating a limitation in the design. Further, in an assembly process, it is easy to be affected by assembly accuracy and variations.
In view of the problems described above, the invention has been developed, and an object of the invention is to provide a circuit breaker having an isolation function in which a handle is not moved to the OFF position when the contact points are stuck, by adding to a switching device with a simple additional part, so that there is no design constraint or no need to assemble accurately.
Further objects and advantages of the invention will be apparent from the following description of the invention.